Process for producing dust free polyvinyl chloride resins

Abstract

The utilization of an air classifier process is effective in separating out fine-sized particles (that is, particles having a size generally less than 75 microns) from a composition of mass produced polyvinyl chloride (PVC) or PVC copolymer resin thereby producing so called normal-sized mass PVC resin particles. Such resultant normal mass PVC resin (fine free) contains very little, if any residual glassy particles and can be utilized for making thermoplastic bottles and other articles requiring low residual vinyl chloride monomer. The removal of the fines also improves the bulk handling characteristics of the normal mass PVC resin. The separated fines constitute a novel blending or extender resin and hence can be utilized in association with a PVC dispersion resin to form a plastisol. The extender resin can also be utilized as a sintering resin, as a drying resin for plasticized dry blends or as an antiblocking resin for PVC compounds.

What is claimed is: 
     
       1. A process for producing an essentially dust free mass PVC resin particles, comprising the steps of: polymerizing vinyl chloride monomers in mass to form discrete particles of PVC resin, and   separating by air classifying said discrete mass PVC resin particles into at least one normal resin portion and a fine-sized portion by removing said fine-sized portion therefrom, said fine-sized portion having particle sizes of approximately 75 microns or less, and wherein said discrete PVC resin has at least 99% by weight of fine-sized particles having a size of 75 microns or less removed therefrom.   
     
     
       2. A process according to claim 1, wherein at least 90% of said fine-sized portion is 45 microns or smaller. 
     
     
       3. A process according to claim 2, wherein said amount of removed fine-sized particles is at least 95% by weight based upon the total amount of fine-sized particles having a size of 75 microns or less in said discrete PVC resin. 
     
     
       4. A process according to claim 3, including simultaneously separating said normal resin portion and said fine-sized portion from said discrete mass PVC resin particles. 
     
     
       5. A process according to claim 4, wherein said normal resin portion has an increased apparent bulk density of at least 4.0% and a funnel flow time reduction of at least 14% in comparison with said discrete mass PVC resin particles. 
     
     
       6. A process according to claim 2, including utilizing a cyclone in association with said air classifier to separate said fine-sized portion. 
     
     
       7. A process according to claim 4, including utilizing a cyclone in association with said air classifier to separate said fine-sized portion.